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Nugget 5: Ballistic Transport in Insb Quantum Wells

This experiment is the first demonstration of ballistic transport in InSb. Related effects have been observed in GaAs structures at liquid-helium temperatures, but they disappear at higher temperatures. Because the high-temperature (>77K) mobility of electrons in InSb is higher than in GaAs, ballistic effects in InSb are expected to persist to higher temperatures. At 140K, the highest temperature studied so far, we find that the bend resistance is undiminished from its value at liquid-helium temperatures. Increasing the operating temperature is an important step towards realizing practical devices based on ballistic transport.
This experiment also marks the beginning of a collaborative effort between NTT and the Center to fabricate and study nanostructure devices based on InSb quantum wells. Nanostructures are fabricated using electron beam lithography and reactive ion etching facilities at NTT. The InSb quantum-well material is grown at one of the Center’s molecular beam epitaxy laboratory.

--- S.J. Chung, N. Goel, M.B. Santos (CSPIN)
K. Suzuki, S. Miyashita, Y. Hirayama (NTT Basic Research Laboratories)

 

Figure 1:Terminals are 0.5mm apart
The so-called bend resistance is measured between two adjacent terminals [2 and 1] while a current is applied between the other two terminals [3 and 4] in a four-terminal structure. The conducting layer is a remotely-doped InSb quantum well with an electron density of 2.66x1011cm-2 and a mobility of 168,000cm2/Vs. The distance L between opposite terminals is 0.2 microns or 0.5 microns.

Figure 2: Ballistic transport across 0.5mm at 185 K
 The bend resistance, Rbend = V2,1 / I3,4 at 1.5K is plotted as a function of applied magnetic field B. The negative resistance at B=0 is a signature of ballistic transport. It is due to electrons traveling ballistically from terminal 4 to terminal 2. For non-ballistic transport, the resistance would be positive as electrons moved diffusively from terminal 4 to terminal 3. From these data, a minimum value of 0.5 microns is deduced for the electron mean free path.